Fire detectors

ABSTRACT

A device for detecting the outbreak of a fire in say, a mine, comprising a housing through which products of combustion can pass. A lamp and a light detector are located on opposite sides of the housing so that light rays are transmitted through the housing to the detector. An interference filter is located between the lamp and the light detector and is designed to pass only light rays having a wave-length corresponding to one of the characteristic wave-lengths of a selected gaseous combustion product such as carbon dioxide. When the combustion product enters the housing energy passes from the light rays to the combustion product and the intensity of the light rays impinging on the light detector thus decreases. This decrease is detected to energize an alarm or the like.

United States Patent 1191 Anderson 1 451 Nov. 18, 1975 1 FIRE DETECTORS [76] Inventor: Quinn Shumway Anderson,

Goldsand, Twist and Smit Sts., J oubert Park, Johannesburg, Transvaal, South Africa [22] Filed: Sept. 10, 1973 [21] Appl. No.: 395,747

[30] Foreign Application Priority Data [58] Field of Search 340/237; 356/51, 204, 206, 356/207; 219/354, 553

[56] References Cited UNITED STATES PATENTS 1,695,031 12/1928 Schmick 340/237 R 2,170,435 8/1939 Sweeney 356/51 X 3,102,257 8/1963 Miller 340/237 R 3,279,308 10/1966 Bartz et a1. 356/51 3,435,209 3/1969 Keahl 356/51 X 3,539,770 11/1970 Wallace 219/553 X Watts. Jr 219/354 x Little 356/206 X Primary Examiner-John W. Caldwell Assistant E.raminer--Daniel Myer Attorney, Agent, or FirmSi1verman & Cass, Ltd.

[57] ABSTRACT A device for detecting the outbreak of a fire in say, a mine, comprising a housing through which products of combustion can pass. A lamp and a light detector are located on opposite sides of the housing so that light rays are transmitted through the housing to the detector. An interference filter is located between the lamp and the light detector and is designed to pass only light rays having a wave-length corresponding to one of the characteristic wave-lengths of a selected gaseous combustion product such as carbon dioxide.

When the combustion product enters the housing energy passes from. the light rays to the combustion product and the intensity of the light rays impinging on the light detector thus decreases. This decrease is detected to energize an alarm or the like.

2 Claims, 1 Drawing Figure DFDIK umamoaom FIRE DETECTORS This invention relates to fire detectors.

It is becoming more and more important, particularly in mines, to be able to pin-point a fire as soon as possible after the outbreak thereof.

Several types of fire detectors have been developed for this purpose. To the best of the Applicants knowledge, however, these known detectors tend to be oversensitive to ambient atmospheric conditions unrelated to combustion with the result that spurious energization of the detectors frequently takes place.

It is an object of the present invention to provide a new and improved type of fire detector.

A fire detector according to the invention comprises a housing, a source of light energy in the housing adapted to transmit light rays across the housing including a filament consisting of a thin ribbon of oxidized nickel chromium alloy and means to pulse the filament at a frequency of the order of 17 Hz, said source, one or more openings in the housing through which products of combustion can enter the housing, a suitable light detector located in the path of the light rays,

light energy and the light detector and adapted to pass to the light detector only light rays having a selected wave-length, and means responsive to the intensity of the light rays impinging on the light detector to operate an alarm.

Further according to the invention the interference filter means is adapted to pass to the light detector only light rays having a wave-length corresponding to one of the characteristic wave-lengths of a selected gaseous combustion product.

Further according to the invention the selected gaseous combustion product is carbon dioxide and the particular wave-length is the 4.27 micron fundamental absorption band.

Further according to the invention the source of light energy is a lamp having a filament which is pulsed at a frequency of the order of 17 Hz.

Further according to the invention the filament consists of a thin ribbon of oxidized nickel-chromium alloy.

To illustrate the invention an embodiment thereof is described hereunder with reference to the accompanying drawing which is a sectional diagrammatic view of a fire detector according to the invention.

In the drawing, a cylindrical housing is provided. A first concave reflector 12 is located at one end of the housing. A suitable lamp 14 is located at the centre point of the reflector. A second concave reflector 16 is located in the housing a short distance away from the first reflector and facing it. The lamp in the first reflector is located at the focal point of the second reflector.

Since alternating signals are easier to process than nonaltemating signals the lamp preferably incorporates a filament which is pulsed at a frequency of the order of 17 Hz via signals from an oscillator 15. The filament itself is preferably a thin ribbon of oxidized Nickelchromium alloy. This alloy is ideal in many respects. Its electrical resistivity is high, its oxidized emissivity is 0.80 to 0.90 over a broad spectral range, it is largely inert chemically and it is physically strong.

A window (sapphire or the like) 18 is located at the centre point of the second reflector 16 to seal the chamber defined by the two reflectors and cylinder.

From the first reflector the rays will again be reflected out of the window 18.

The light rays 20 emerging from the window 18 are arranged to impinge on a suitable light detector 22 such as an Indium Antimonide Photoelectric detector. A suitable interference filter 24 is located immediately in front of the detector 22 to pass only light rays having a wavelength corresponding to one of the characteristic wave-lengths of a selected gaseous combustion product.

In a preferred form of the invention the interference filter 24 is designed to pass only light rays having a wave-length corresponding to one of the characteristic wave-lengths of carbon dioxide such as the 4.27 micron fundamental absorption band.

The output of the detector 22 is fed to any suitable electronic device so that any substantial change in the magnitude of the current from the detector is caused to actuate a suitable alarm. By way of example only, an amplifier 23 and alarm 25 are shown.

In use, the fire detector of the invention is located for example in a mine. With no combustion the intensity of lnterference filter means located between the source of 25 the light rays passing through the filt 24 will be f a certain value at which the alarm is not actuated. When combustion takes place, carbon dioxide will enter the chamber through suitable openings 26. Energy will pass from the light rays in the chamber to the carbon dioxide and the intensity of the light rays impinging on the detector will thus decrease. This decrease is detected by the electronic device and the alarm is actuated.

Generally the output from the detector would be amplified before being fed to the electronic detecting device. To overcome the problem of signal attenuation due to dirty reflectors, dust etc. a sample of the light rays could be taken (at a different wave-length from those passing through the filter) and this could be used to adjust the gain of the amplifier to compensate for the attenuation.

The electronic device receiving the output of the de tector 22 may be of a differential type so that, with only atmospheric carbon dioxide present, there is no output from the electronic device. In the presence of a fire, however, the resulting carbon. dioxide will cause a voltage to exist at the output of the electronic device.

I claim:

1. A fire detector comprising a housing, a source of light energy in the housing adapted to transmit light rays across the housing, the source comprising a lamp having a filament consisting of a thin ribbon of oxidized nickel chromium alloy, means to pulse the filament at a frequency of the order of 17 Hz, at least one opening in the housing through which products of combustion can enter the housing, said products of combustion affecting the intensity of said light rays, a light detector located in the path of the light rays, interference filter means located between the source of light energy and the light detector and adapted to pass to the light detector only the light rays having a wavelength corresponding to one of the characteristic wavelengths of carbon dioxide, and means responsive to the intensity of the light rays impinging on the light detector to operate an alarm.

2. A fire detector as claimed in claim 1 in which said characteristic wavelength is the 4.27 micron fundamental absorption band. 

1. A FIRE DETECTOR COMPRISING A HOUSING, A SOURCE OF LIGHT ENRGY IN THE HOUSING ADAPTED TO TRANSMIT LIGHT RAYS ACROSS THE HOUSING, THE SOURCE COMPRISING A LAMP HAVING A FILAMENT CONSISTING OF A THIN RIBBON OF OXIDIZED NICKEL CHROMIUM ALLOY, MEANS TO PULSE THE FILAMENT AT A FREQUENCY OF THE ORDER OF 17 HZ, AT LEAST ONE OPENING IN THE HOUSING THROUGH WHICH PRODUCTS OF COMBUSTION CAN ENTER THE HOUSING, SAID PRODUCTS OF COMBUSTION AFFECTING THE INTENSITY OF SAID LIGHT RAYS, A LIGHT DETECTOR LOCATED IN THE PATH OF THE LIGHT RAYS, INTERFERENCE FILT ER MEANS LOCATED BETWEEN THE SOURCE OF LIGHT ENERGY AND THE LIGHT DETECTOR AND ADAPTED TO PASS TO THE LIGHT DETECTOR ONLY THE LIGHT RAYS HAVING A WAVELENGTH CORRESPONDING TO ONE OF THE CHARACTERISTIC WAVELENGTH OF CARBON DIOXIDE, AND MEANS RESPONSIVE TO THE INTENSITY OF THE LIGHT RAYS IMPINGING ON THE LIGHT DETECTOR TO OPERATE AN ALARM.
 2. A fire detector as claimed in claim 1 in which said characteristic wavelength is the 4.27 micron fundamental absorption band. 